What model are you trying to use? This should appear when you're using anything below SiS 496 and it can appear on some machines if you have both a SBPCI and an ethernet card going.

It got me when I tried to use Trio64 with the WinBIOS 486 (ISA/VLB only) since that's what I use on my real board (though to be fair mine's a certain infamous buggy vip board that would be fictionally too great if it were to be emulated)